Approximately 3 million residents are served by public water systems that use groundwater, and more than 2.9 million Michigan residents draw groundwater through a private well.
Groundwater is stored in aquifers, which are spaces below ground in which water is trapped within layers of sand and gravel. The water stored in aquifers originates as rain and snowmelt that flows downward from the surface through the different layers of soil. This movement acts as a natural filtration system and removes many of the harmful particles accumulated from the surface. Water flows until it reaches bedrock, there, the water fills the open spaces between the sediment grain, saturating the soil and acting as storage for the fresh, filtered water.
The depth and availability of groundwater depends heavily on type of soil and minerals present in the local area. Some areas may be situated on very dense rocks that trap and pressurize the groundwater creating flowing springs, or artesian aquifers. Other areas may be located on looser soil that easily allows water to pass through.
The amount of precipitation and the amount of water pumped from an aquifer has a significant impact on the groundwater levels in a given area. If a region does not receive enough precipitation or if a significant amount of water is pumped out, the groundwater may be used faster than it is recharged, or replaced. This can lead to shrinking lakes, dry riverbeds, and the need for deeper wells.
Bedrock: a deposit of solid rock that is typically buried beneath the soil and other broken or unconsolidated material, often containing an underground, confined aquifer (Britannica.com)
Usually as water passes through soil and porous rock it is naturally filtered improving its overall quality. However if manmade and naturally-occurring contaminants are present, groundwater can become contaminated.
Michigan has naturally-occurring deposits of arsenic and nitrate, which may contaminate groundwater as it passes over mineral deposits.
Synthetic chemicals may be released from a variety of sources including underground storage tanks, old gas stations, landfills, improperly handled hazardous materials, agricultural operations or lawn care chemicals.
The Michigan Department of Environmental Quality (MDEQ) has established cleanup standards for more than 300 different chemicals that affect Michigan’s land and groundwater including arsenic, nitrate, and volatile organic compounds (VOCs).
Volatile Organic Compound (VOC): wide range of chemicals that make up materials such as industrial solvents, landfill leachate, and oil spills.
The Michigan Environmental Mapper provides a map of known sites of contamination.
Some contaminated sites have been carefully monitored, while others have little data to show where contamination may have spread. If a property owner knows they have contaminated groundwater that has spread under their neighbor’s property, they are required to notify the owners of the affected properties.
If one of these sites is in your area, and you utilize a private well, regular testing of your water is recommended. In some areas, local ordinances prohibit private wells to ensure the public is not exposed to potential contamination.